1. Field of Invention
The present invention relates to a wavelength division multiplexing and, more particularly, to an optical foreplane for performing wavelength switching, wavelength division multiplexing, and time division multiplexing.
2. Description of Related Art
Time division multiplexing and wavelength conversion functions are performed by prior art optical telecommunication switches. For example, U.S. Pat. No. 5,521,733 discloses an optical switch that utilizes wavelength multiplexing. Wavelength-demultiplexing is often performed with a grating, using a separate grating or regions of gratings for each fiber. Each wavelength of each fiber is then sent to a separate detector, where the optical signal is converted to an electronic signal. The signal is read in electronic form to determine its destination, and the signal is then directed, often at lower bandwidth and in parallel optical interconnections, to an output port where it is converted to the desired wavelength by a transmitter and sent out on the desired fiber.
This process is cumbersome for several reasons. First, massive electrical interconnection is needed between Ni input fibers and Mi input wavelengths to No output fibers and Mo output wavelengths, resulting in a cross-connection that involves Nixc3x97Mi inputs and No xc3x97Mo outputs. In some applications, Ni,o might be 12 or more, and Mi,o might be 100 or more, resulting in an interconnection with 1200 input combinations xc3x971200 output combinations. Electronic cross-connects of these sizes are not now made and are at least an order of magnitude beyond what is now available.
Second, prior-art processes typically require the use of cable, printed-circuit board, or an optical backplane to transfer data to and from the central electronic crossbar. Because of the bandwidths required for the transfer, an optical backplane is currently the preferred means of performing this transfer of information, as currently implemented by, for example, Ciena, Inc. This entails a process of: (1) conversion of the electronic signal to an optical signal, and, via an optical backplane, transmitting the light to a central electronic cross-switch, (2) switching the electronic signals, (3) reconversion of the electronic signal back to light and passing the light again through a backplane to outgoing ports, and (4) electronic reformatting and transmission of the signal to a destination. This process requires six (6) conversions of optical to electronic or electronic to optical signals. Additionally, significant extra hardware is needed for every conversion. It should be noted that this means of switching can perform both wavelength conversion and time division multiplexing if the electronic cross-connect is endowed with means to combine electronic signals from different input ports to a common output port. This implementation can also perform broadcasting if so desired.
Another instance of prior art improves on this approach. In this alternative, the electronic cross-connect is replaced by an optical cross-connect, such as the Lambda-router produced by Lucent, Inc. In this device, the incoming light is wavelength-demultiplexed, and then wavelength-converted to the desired outgoing wavelength, and the light is then routed to the proper output fiber by a large optical cross-connect. This approach is advantageous because it requires only one conversion from optical to electronic and electronic to optical conversion, but requires a prohibitively large optical cross-connect, due to the effects of diffraction, when more than a few dozen fibers are used with eighty (80) or more wavelengths. This approach also has difficulty with broadcasting the signal, unless substantial electronic preprocessing is performed when the signal is in electronic form.
In view of the foregoing, there is a need in the art for a device that permits many thousands of fibers at many hundreds of wavelengths to be interconnected. It would also be advantageous, if the device could transfer information via multiple wavelengths of light, and allow broadcasting to be performed. Additionally, it would be advantageous to allow time division and wavelength division multiplexing to be performed using signals from disparate fibers.
An advantage of the present invention is that it is able to allow multiple autonomous processors to transfer information via multiple wavelengths of light.
Another advantage of the present invention is that it is able to allow multiple processors to multiplex respective optical signals in time.
A further advantage of the present invention is that it is able to eliminate the need for an optical backplane in a specific type of an optical switch, thereby eliminating costly material and complexity from the optical switch.
An additional advantage of the present invention is that it is able to eliminate the need for an optical backplane in more general optical switches that utilize multiple wavelengths.
Another advantage of the present invention is that it is able to provide optical delay and, hence, provide optical buffering in an optical switch.
These and other advantages of the present invention may be realized by reference to the remaining portions of the specification, claims, and abstract.
The present invention includes an optical signal altering device that includes a plurality of optical signal carriers or fibers for communicating an optical signal. The fibers include at least one source and at least one target. The device also includes a plurality of switch elements for receiving an optical signal from a source and transmitting the optical signal to a target. Furthermore, the device includes at least one port adapted to receive an optical signal having a first wavelength from at least one first switch element and transmit an optical signal having a second wavelength.
The above description sets forth, rather broadly, the more important features of the present invention so that the detailed description of the preferred embodiment that follows may be better understood and contributions of the present invention to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and will form the subject matter of claims. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangement of the components set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.